1. Field of the Invention
The invention relates to the technical field of motion estimation and, more particularly, to a method for fast multiple reference frame motion estimation (fast MRF-ME).
2. Description of Related Art
Current video coding standards essentially use motion estimation (ME) to remove the redundancies from an image sequence, thereby obtaining higher image compression performance. In the H.264/MPEG-4 AVC video coding standard, multiple reference frame motion compensation and variable blocksize motion compensation are used to achieve such a high image compression performance.
When multiple reference frame motion estimation (MRF-ME) is used, a picture can be predicted from multiple reference frames. Because each reference frame is used for motion estimation, the computation for MRF-ME is increased rapidly.
U.S. Pat. No. 6,782,052 granted to Shijun, et al. for a “Reference frame prediction and block mode prediction for fast motion searching in advanced video coding” discloses a method of reference frame prediction to determine reference frames. As shown in FIG. 1, reference frames 12, 14 . . . 22 are sequentially arranged along a time axis, wherein the frame 22 is current frame. In FIG. 2, block 26 indicates a target for motion estimation in a current frame, and blocks 28, 30, 32 and 34 are adjacent to the block 26 in the current frame. A predictive reference frame fp has p reference frames away from the current frame, wherein p is determined by an equation p=min(n−1, p0+max(a,b,c,d)). That is, even the number of searched frames is reduced from n to p, the computation is still huge for the MRF-ME to be performed on each of the reference frames from zero to p.
Therefore, it is desirable to provide an improved MRF-ME to mitigate and/or obviate the aforementioned problems.